Safety system for gas burners



Nov. 19, 1963 J. FREGE ETAL 3,111,161

SAFETY SYSTEM FOR GAS BURNERS Filed Jan. 20, 1959 2 Sheets-Sheet 1magnetic push resistance peroiure negufive tern oefficient Wm M Z i]: BYMMW W5,

Nov. 19, 1963 J. FREGE ETAL 3,111,161

SAFETY SYSTEM FOR GAS BURNERS Filed Jan. 20, 1959 2 Sheets-Sheet 2magnetic push mm ham KW Fig.|a

United States Patent 3,111,161 SAFETY SYSTEM FOR GAS BURNERS JohannesFrege, Hasslinghausen Usher, and Kurt Saehse,

Gevelsherg, Westphalia, Germany, assignors to W.

Kreift Alrtiengesellsehaft, Gevelsherg, Westphalia, Germany Filed .llau.2t), 1%), Ser. No. lililfidl 6 Claims. (Cl. 15-125) This inventionrelates to safety systems for gas burners, and lends itself to gasheating systems of any kind, particularly gas ranges.

It is a general object of this invention to improve prior art safetysystems for gas ranges.

This invention is concerned with gas heating systems which are free fromthe dangers normally resulting from a temporary reduction of gaspressure, or a temporary interruption of the supply of gas, and theobject of the present invention is to achieve this end with simpler andmore effective means than in prior art gas ranges.

When a pilot burner fails to ignite a main burner, and gas is allowed toescape under such conditions through the main burner, the gas forms ahighly explosive and generally toxic mixture with ambient air. Suchmixtures tend to endanger life due to the toxicity thereof, and maycause great damage when accidentally ignited.

It is another object of this invention to provide gas heating systemshaving semi-automatic controls positively precluding the unintentionalescape of gas from non-ignited gas burners, and thus precludingformation of dangerously toxic and/or explosive mixtures of gas and air.

Still another object of the invention is to provide gas heating systemswherein the main burner is provided with a pilot burner for igniting themain burner and with means responsive to the radiation emitted from thepilot burner which means, in turn, control interlocks adapted to assuresafe operation of the heating system.

Still anoth r object of the invention is to provide means foraccelerating certain changeover switching operations which are necessaryto achieve the aforementioned ends.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to theaccompanying drawings wherein FIG. 1 is a dia' rammatic representationof a gas range embodying the invention;

FIG. la is a diagrammatic representation of a modified version of therange shown in FIG. 1.

Referring now to FIG. 1, numeral 2 has been applied to generallyindicate a transformed having three secondary windings 2', 2", 2 Theprimary circuit, or supply circuit, of transformer 2 includes fuse 1 andswitching device it. Winding 2' feed by means of leads 1%, lit? thefilament 3 of thyratron 3. Winding 2' is connected to a rectifier 5 madeup of two rectifier cells. The DC. output circuit of rectifier 5energizes solenoid valves 12, 14 and when the winding of relay orchange-over relay 6' is energized. Relay 6' comprises a pair of movablecontacts 6a, 6b. Contact 6a is adapted to cooperate with a pair of fixedcontacts 6a of which the right contact is a blind contact i.e. a contactnot connected to any circuit terminal. Contact 6]) is adapted tocooperate with a pair of fixed contacts 612 of which the left is a blindcontact. When the winding of relay 6 is energized the two contacts 6a,6b controlled by relay 6' are in the right position thereof and the loadcircuit of rectifier 5 runs as follows: Center tap ltlti between the tworectifier cells 5; movable contact 611; right fixed contact 627'; leada, relay 17 and solenoid valves 12, idand 15 in parallel; lead [1; andcenter tap of trans former Winding 2". When relay 6' is not energizedthe movable contacts 6a, 6b controlled by relay 6 are in the leftposition thereof and then transformer winding 2" applies an A.-C.voltage to three serially connected igniters '7 of the incandescent typeof which each is associated with one of three pilot burners '7. Thecircuit of igniters 7 when closed runs as follows: Upper terminal ofwinding 2; lead c; movable contact 6a; left fixed contact 6a; all threeigniters 7 in series; lead d; lower end of secondary winding 2". Thethree pilot burners '7' are supplied with gas by line T branching oifmanifold M to which cooking burners or main burners B are connected bythe intermediary of solenoid valves 12, 14, 15. Transformer winding 2"is connected to a rectifier bridge circuit 4 whose D.-C. output circuitincludes leads 111 and 1?.2 and two resistors 9, it forming apotentiometer. Resistors 9, Jill are shunted by a capacitor 22 fordecreasing ripples in the output of rectifier 5. The grid bias of tube 3is taken from potentiometer 9, 1h. The grid circuit of tube 3 includesserially connected resistors 8 having a negative temperature coefficientof resistance and also includes resistors 19, Ztl and 21. Each ofresistors is arranged immediately adjacent one of pilot burners 7 andexposed to the heat radiated therefrom. Resistors 8 are connected bylead 2 to the point of potentiometer 9, it) between resistors 9 and 10and resistors i9, 20 and 21 are connected by lead 1 to the negativeterminal of potentiometer 9, 16. Resistors l9 and it are adjustablemaking it possible to negatively bias the control grid 3" of thyratron3, thus precluding any flow of plate current. Resistor 23 arrangedimmediately adjacent to the control grid 3" of thyratron 3 is a gridlimiting resistor provided for grid protection. Grid 3" of thyratron 3is conductively connected to the cathode 3 thereof. Manifold M comprisesa manually operable cock R for admitting gas to cooking or main burnersB and pilot burners '7'. This cool: which is arranged at a pointupstream from the point where line T branches off manifold M ismechanically coupled with switch it in the primary circuit oftransformer 2 in such a way that when gas is being admitted to pilotburners 7' by opening that valve, the primary or energizing circuit oftransformer Z is being closed simultaneously by closing switch 1. As aresult of energizing transformer 2 igniters 7 become immediatelyincandescent and ignite the combustible gas escaping at the pilotburners 7. The heat generated at pilot burners '7 is transferred toresistors 8, as the result of which their resistance instantlydecreases. This, in turn, reduces the negative grid bias of tube 3,causing the flow of a current in the plate circuit. This circuit incl.des plate or anode 3", lead g and resistor it in addition to theaforementioned relay 6 and leads 103 and 1532. The latter and lead theare connected to the terminals of transformer winding 2". Resistor l8shunts relay 5 when contact 17 under the control of relay 17 is in theleft position thereof. The shunt across relay 6' includes lead [2,movable contact 17', resistor 18 and lead 1'.

The operation or" the arrangement of FIG. 1 is as follows:

Because of the mechanical coupling of the aforementioned cock R foradmitting gas to manifold M and line T with switch 1, transformer 2 isalways energized concornitant with admission of gas to the system. Uponadmittance of gas to the system the gas escaping from pilot burners 7'is ignited by igniters 7. The heat radiated from pilot burners 7 resultsin a decrease of the resistance of resistors 8 directly included in thecircuit of control grid 3 of tube 3. This swings the bias of grid 3"from negative to positive and initiates the flow in FIG. 1 to their rig.t position.

of plate current. The latter energizes relay 6', causing its twochange-over contacts 6a, as to shift from their left position to theirright position. This causes opening of the circuit of igniters 7 andclosing of the circuit of solenoid valves l2, l4, l5 and opening of thelatter and energizing of relay 17. The gas escaping at main burners Bupon opening of solenoid valves 12, l4, is ignited by pilot burners 7.Energization of relay 17 causes movement of contact 17' from its rightposition to its left position, thus shunting resistor l3 across relay 6.

Relay 6', i.e. the operating winding thereof, is energized by themaximum plate current which thyratron 3 is capable of supplying, andthus contacts 6a, 6b are rapidly moved against their bias from theirleft position shown A smaller magnetic action is required to maintaincontacts 6a, 6b in their right position than to rapidly move the same totheir right position. Hence relay winding 6' may be de-energized to someextent after contacts 6a, 6b have completed their travel to their rightposition. This accelerates their movement to their left position as aresult of a renewal of a cut-off of thyratron 3 and cessation of theflow of its plate current.

The flames at burners B may be turned off in different ways. All burnersB may be turned off by closing the aforementioned cock R in manifold M,simultaneously de-energizing transformer 2. Then the entire system,including all its electrical components, is inoperative. As long aspilot burners 7 burn, the flame on any burner B will be re-ignited whenthe respective burner is being resupplied with gas. As soon as one ormore of pilot burners 7' are extinguished, the temperature of one ormore resistors 8 decreases and, therefore, the bias of control grid 3"tends to become negative, to interrupt the flow of plate current anddeenergize relay 6, causing both contacts 6a, 6b to move from theirright positions to their left positions illustrated in P16. 1. Thiscauses interruption of the circuits of solenoid valves 1.2, 14-, 15 andclosing of these valves, and it also causes closing of the circuit ofigniters 7 and the igniters to become incandescent. Shunting of relay dby contact 17 and resistor it; accelerates the changeover operation ofrelay 6' when the bias of grid 3" swings from positive to negative sinceit diverts a portion of the plate current of tube 3 from relay 6.

The arrangement of parts of FIG. la is substantially the same as thatshown in FIG. 1 and the same reference characters have been applied inFIGS. 1 and in to indicate like parts. Hence the arrangement of FIG. 1acalls only for an additional description inasmuch as it deviates fromthat shown in FIG. 1.

FIG. la illustrates another shunt arrangement causing a portion of theplate current of tube 3 to by-pass relay 6'. The arrangement shown inFIG. 1a may, if desired, take the place of parts l7, 17', 18 of FIG. 1.According to FIG. la relay 6' is shunted by two variable resistors l8,18'. The latter has a high negative temperature coefficient ofresistance. The plate current of tube 3 flows in parallel paths throughrelay 6 and resistors 13 and 1S". Resistor 18" is heated by z' -r lossesas a result of the how of current through it, causing its resistance todecrease and to carry a progressively increasing portion of the totalplate current of tube 3. In other words, relay 6' is being progressivelydeenergized by resistor 18", thus accelerating the change-over ofcontacts 6a, 6b from their right positions to their left positions oncooling of resistors 8.

Interruption of the gas service causes simultaneous extinction oi themain burners B and of the pilot burners 7'. Therefore resistors 3 cooldown, their resistance increases, the bias of grid 3" swings frompositive to negative and interrupts the flow of plate current throughdischarge tube 3. This deeuergizes relay 6' causing contacts 6a, db tomove from right to left and to close the circuit of igdniters '7.Therefore pilot burners 7' will be ignited whenever service is restoredand gas escapes at the nozzle of pilot burners 7 N T he same sequence ofsteps occurs whenever one of the main burners should be extinguished bya draft. It is possible to manufacture resistors having a negativetemserature coefficient of resistance and changing their resistancedrastically at the occurrence of relatively small changes in temperaturein sub-miniature size.

It will be observed that the circuitry of FIGS. 1 and.

la involves three separate and distinct stages: (1) The grid circuit ofthyratron 3 including sensing resistors 8', (2) the energizing circuitof relay 6 which is identical with the plate circuit of thyratron 3; and(3) the circuits of solenoid valves l2, l4, l5 and electric igniters 7.As nienttioned, these three stages are separate and in the abovesequence each of the three stages is adapted to carry increasinglylarger currents and each stage involves an increasingly larger power.

The combinaiton of a temperature sensing element in the form of aresistor having a negative temperature coellicient of resistance with athyratron yields an extremely critical or sensitive on-olfcharacteristic which could neither be achieved by combining atemperature sensing element in the form of a resistor having a positivetemperature coefiicient of resistance with a thyratron or by combining atemperature-sensing element in the form of a resistor having a negativecoefficient of resistance with a grid-controlled high vacuum electrontube.

Since the thyratron 3 carries either its full plate current or no platecurrent at all, relay 6' will either be fully energized, orde-energized, depending upon the condition the thyratron 3 is in. Inother words, the operation of contacts 6a, 6b of relay 6 is positive andis not affected by mechanical properties such as inaccuracies of relay6'.

The coaction between temperature sensing elements in form of resistors 8having a negative temperature coer cient of resistance with a thyratronis a pre-requisite for providing a series arrangement of such sensingresistors 8 of which each is associated with a pilot burner 7' and eachcontrols the operation of relay 6' and that of its movable contacts 6a,db. A change in the resistance of each of resistors 8 is but arelatively small change in the aggregate resistance of all resistors 25,and if the change of the resistance of one single resistor 53 due to arelatively small change in temperature would not sufilce to swing thebias of thyratron 3 so as to fully open or fully close the same, theabove series connection of all sensing resistors 8 would be impossible.

It will also be understood that we have illustrated and described hereintwo preferred embodiments of our invention and tnat various alterationsmay be made in the details thereof without departing from the spirit andscope of our invention as defined in the appended claims.

We claim:

1. A gas distribution system comprising in combination:

(a) a manifold;

(b) a main gas burner supplied with gas from said manifold;

(c) an electromagnetic valve having a de-energized closed position andan energized open position admitting gas from said manifold to said mainburner;

(d) a pilot burner supplied with gas from said manifold and operativelyrelated to said main burner;

(e) an electric igniter operatively related to said pilot burner;

(f) an electromagnetic change-over relay for controlling said valve andsaid igniter and including an operating winding, said relay having afirst position upon de-energization of said operating winding adapted tocause de-energization of said valve and energization of said igniter andsaid relay having a second position upon energization of said operating#3 winding adapted to cause energization of said valve andde-energization of said igniter;

(g) a thyratron having a plate circuit including said operating windingand a grid circuit including a control grid;

(h) means for biasin said grid sufificiently negatively to inhibit theflow of current in said plate circuit as long as the resistance in saidgrid circuit exceeds a predetermined value;

(i) a temperature sensing resistor having a negative temperaturecoefiicient of resistance exposed to heat radiation emitted from saidpilot burner arranged in said grid circuit; and

(j) means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means including normally ineffective shunt means acrosssaid operating winding of said relay adapted to become effective onlyupon completion of the movement of said relay from said first positionthereof to said second position thereof.

2. A gas distribution system comprising in combination:

(a) a manifold;

(b) a main gas burner supplied with gas from said manifold;

(c) an electromagnetic valve having a de-energized closed position andan energized open position admitting gas from said manifold to said mainburner;

(d) a pilot burner supplied with gas from said manifold and operativelyrelated to said main burner;

(e) an electric igniter operatively related to said pilot burner;

(1) an electromagnetic change-over relay for controlling said valve andsaid igniter and including an operating winding, said relay having afirst position upon de-energization of said operating winding adapted tocause de-energization of said valve and energization of said igniter andsaid relay having a second position upon energization of said operatingwinding adapted to cause energization of said valve and de-energizationof said igniter;

(g) a thyratron having a plate circuit including said operating windingand a grid circuit including a control grid;

(12) means for biasing said grid sufiiciently negatively to inhibit theflow of current in said plate circuit as long as the resistance in saidgrid circuit exceeds a predetermined value;

(i) a temperature sensing resistor having a negative temperaturecoefiicient of resistance exposed to heat radiation emitted from saidpilot burner arranged in said grid circuit; and

(7) means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means including an additional electromagnetic relay adaptedto be energized in response to completion of the movement of said firstmentioned relay from said first position thereof to said second positionthereof; and

(k) said accelerating means further including means for shunting saidoperating winding in response to energization of said additional relay.

3. A gas distribution system comprising in combination:

(a) a manifold;

(b) a main gas burner supplied with gas from said manifold;

(c) an electromagnetic valve having a de-energized closed position andan energized open position admitting gas from said manifold to saidburner;

(d) a pilot burner supplied with gas from said manifold and operativelyrelated to said main burner;

(e) an electric igniter operatively related to said pilot burner;

(1) an electromagnetic change-over relay for controlling said valve andsaid igniter and including an op erating winding, said relay having afirst position upon de-energization of said operating winding adapted tocause de-cnergization of said valve and energization of said igniter andsaid relay having a second position upon energization of said operatingwinding adapted to cause energization of said valve and de-energizaitonof said igniter;

(g) a thyratron having a plate circuit including said operating Windingand a grid circuit including a control grid;

(11) means for biasing said grid sufficiently negatively to inhibit theflow of current in said plate circuit as long as the resistance in saidgrid circuit exceeds a predetermined value;

(i) a temperature sensing resistor having a negative temperaturecoefficient of resistance exposed to heat radiation emitted from saidpilot burner arranged in said grid circuit; and

(1') means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means including means establishing a shunt across saidoperating Winding of said relay, said shunt-establishing means includinga resistor having a negative temperature coefiicient of resistance.

4. A gas distribution system comprising in combination:

(a) amanifold;

(b) a plurality of main gas burners connected in parallel and suppliedwith gas from said manifold;

(c) a plurality of electromagnetically operated valves each arrangedbetween said manifold and one of said plurality of main burners and eachhaving a closed position and an open position admitting gas from saidmanifold to said one of said plurality of main burners;

(d) a plurality of pilot burners supplied with gas from said manifoldeach operatively related to one of said plurality of main burners;

(e) a plurality of electric igniters serially connected into an ignitercircuit and each operatively related to one of said plurality of pilotburners;

(f) an electromagnetic change-over relay for controlling said pluralityof valves and said plurality of igniters and including an operatingwinding, said relay having a first position upon de-energization of saidoperating winding adapted to cause closing of said plurality of valvesand energization of said plurality of igniters and said relay havin asecond position upon energization of said operating winding adapted tocause opening of said plurality of valves and deenergization of saidplurality of igniters;

(g) a thyratron having a plate circuit including said operating Windingand having a grid circuit including a control grid;

(h) means for sufficiently negatively biasing said control grid toinhibit the flow of current. in said plate circuit as long as theresistance of said grid circuit exceeds a predetermined value.

(1') a plurality of temperature sensing resistors having a negativetemperature coefiicient of resistance serially connected in said gridcircuit each exposed to heat radiation emitted from one of saidplurality of pilot burners and each adapted to inhibit the flow ofcurrent in said plate circuit and energization of said operating windingupon extinction of but one of said plurality of pilot burners andconcomitant increase of said resistance of said grid circuit; and

(j) means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means int eluding means responsive to the flow of currentin said plate circuit for establishing a shunt across said operatingwinding of said relay upon movement of said relay from said firstposition thereof to said second position thereof. 5. A gas distributionsystem comprising in combination:

(a) amanifold;

(b) a plurality of main gas burners connected in parallel and jointlysupplied with gas from said manifold;

(c) a plurality of electromagnetically operated valves each arrangedbetween said manifold and one of said plurality of main burners and eachhaving a closed position and an open position admitting gas from saidmanifold to said one of said plurality of main burners;

(d) a plurality of pilot burners jointly supplied with gas from saidmanifold each operatively related to one of said plurality of mainburners;

(e) a plurality of electric igniters serially connected into an ignitercircuit and each operatively related to one of said plurality of pilotburners;

(1) an electromagnetic change-over relay for controlling said pluralityof valves and said plurality of igniters and including an operatingwinding, said relay having a first position upon de-energization of saidoperating winding adapted to cause closing of said plurality of valvesand energization of said plurality of igniters and said relay having asecond position upon energization of said operating winding adapted tocause opening of said plurality of valves and deenergization of saidplurality of igniters;

(g) a thyratron having a plate circuit including said operating windingand having a grid circuit including a control grid;

(h) means for biasing said control grid sufiiciently negatively toinhibit the flow of current in said plate circuit as long as theresistance of said grid circuit exceeds a predetermined value;

(1') a plurality of temperature sensing resistors having a negativetemperature coefiicient of resistance serially connected in said gridcircuit each exposed to heat radiation emitted from one of saidplurality of pilot burners and each adapted to inhibit a flow of currentin said plate circuit and energization of said operat ing Winding uponextinction of but one of said plurality of pilot burners and concomitantincrease of said resistance of said grid circuit; and

(j) means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means including an additional electromagnetic relay adaptedto be energized in response to completion of the movement of said firstmentioned relay from said first position thereof to said second positionthereof, said accelerating means further including means for shuntingsaid operating winding of said relay in response to energization of saidadditional relay.

6. A gas distribution system comprising in combination:

(a) amanifold;

(b) a plurality of main gas burners connected in parallel and jointlysupplied with gas from said manifold.

(c) a plurality of electromagnetically operated valves each arrangedbetween said manifold and one of said plurality of main burners and eachhaving a closed position and an open position admitting gas from saidmanifold to said one of said plurality of main burners;

(d) a plurality of pilot burners jointly supplied with gas from saidmanifold each operatively related to one of said plurality of mainburners;

(e) a plurality of electric igniters serially connected into an ignitercircuit and each operatively related to one of said plurality of pilotburners;

(f) an electromagnetic change-over relay for controlling said pluralityof valves and said plurality of igniters and including an operatingwinding, said relay having a first position upon deenergization of saidoperating winding adapted to cause closing of said plurality of valvesand energization of said plurality of igniters and said relay having asecond position upon energization of said operating winding adapted tocause opening of said plurality of valves and de-energization of saidplurality of igniters;

(g) a thyratron having a plate circuit including said operating windingand having a grid circuit including a control grid;

(It) means for biasing said control grid sufficiently negatively toinhibit the flow of current in said plate circuit as long as theresistance of said grid circuit exceeds a predetermined value;

(i) a plurality of temperature sensing resistors having a negativetemperature coefficient of resistance serially connected in said gridcircuit each exposed to heat radiation emitted from one of saidplurality of pilot burners and each adapted to inhibit a flow of currentin said plate circuit and energization of said operating winding uponextinction of but one of said plurality of pilot burners and concomitantincrease of said resistance of said grid circuit; and

(j) means for accelerating the switching operation of said relay fromsaid second position thereof to said first position thereof, saidaccelerating means including means establishing a shunt across saidoperating winding of said relay, said shunt-establishing-means includinga resistor having a negative coeflicient of temperature.

References Cited in the file of this patent UNITED STATES PATENTS1,858,265 Dahlstrorn May 17, 1932 2,212,352 Plein Aug. 20, 19402,327,690 Ackerman Aug. 24, 1943 2,411,642 Strobel Nov. 26, 19462,448,475 Strobel et a1. Aug. 31, 1948 2,479,797 Wasser Aug. 23, 19492,511,881 Snyder June 20, 1950 2,608,609 Fitch Aug. 26, 1952 2,614,621Main Oct. 21, 1952 2,624,398 Thomson Jan. 6, 1953 2,839,132 Blackett etal. June 17, 1958 2,924,270 Deziel Feb. 9, 1960

1. A GAS DISTRIBUTION SYSTEM COMPRISING IN COMBINATION: (A) A MANIFOLD;(B) A MAIN GAS BURNER SUPPLIED WITH GAS FROM SAID MANIFOLD; (C) ANELECTROMAGNETIC VALVE HAVING A DE-ENERGIZED CLOSED POSITION AND ANENERGIZED OPEN POSITION ADMITTING GAS FROM SAID MANIFOLD TO SAID MAINBURNER; (D) A PILOT BURNER SUPPLIED WITH GAS FROM SAID MANIFOLD ANDOPERATIVELY RELATED TO SAID MAIN BURNER; (E) AN ELECTRIC IGNITEROPERATIVELY RELATED TO SAID PILOT BURNER; (F) AN ELECTROMAGNETICCHANGE-OVER RELAY FOR CONTROLLING SAID VALVE AND SAID IGNITER ANDINCLUDING AN OPERATING WINDING, SAID RELAY HAVING A FIRST POSITION UPONDE-ENERGIZATION OF SAID OPERATING WINDING ADAPTED TO CAUSEDE-ENERGIZATION OF SAID VALVE AND ENERGIZATION OF SAID IGNITER AND SAIDRELAY HAVING A SECOND POSITION UPON ENERGIZATION OF SAID OPERATINGWINDING ADAPTED TO CAUSE ENERGIZATION OF SAID VALVE AND DE-ENERGIZATIONOF SAID IGNITER; (G) A THYRATRON HAVING A PLATE CIRCUIT INCLUDING SAIDOPERATING WINDING AND A GRID CIRCUIT INCLUDING A CONTROL GRID; (H) MEANSFOR BIASING SAID GRID SUFFICIENTLY NEGATIVELY TO INHIBIT THE FLOW OFCURRENT IN SAID PLATE CIRCUIT AS LONG AS THE RESISTANCE IN SAID GRIDCIRCUIT EXCEEDS A PREDETERMINED VALUE; (I) A TEMPERATURE SENSINGRESISTOR HAVING A NEGATIVE TEMPERATURE COEFFICIENT OF RESISTANCE EXPOSEDTO HEAT RADIATION EMITTED FROM SAID PILOT BURNER ARRANGED IN SAID GRIDCIRCUIT; AND (J) MEANS FOR ACCELERATING THE SWITCHING OPERATION OF SAIDRELAY FROM SAID SECOND POSITION THEREOF TO SAID FIRST POSITION THEREOF,SAID ACCELERATING MEANS INCLUDING NORMALLY INEFFECTIVE SHUNT MEANSACROSS SAID OPERATING WINDING OF SAID RELAY ADAPTED TO BECOME EFFECTIVEONLY UPON COMPLETION OF THE MOVEMENT OF SAID RELAY FROM SAID FIRSTPOSITION THEREOF TO SAID SECOND POSITION THEREOF.